Doubts about the reality of global warming that were significant half a dozen years ago have today shrunk to zero, leaving only denialists and fossil-industry lobbyists in opposition.

A steady drumbeat of data confirms the rise in Earth's surface temperature and the part played by oil, gas and coal, whose invisible carbon pollution traps the Sun's heat, in effect creating a global greenhouse.

Scientists report melting sea ice around the North Pole, shrivelling glaciers in Greenland and Europe, retreating permafrost in Siberia and progressive acidification of the seas from atmospheric carbon dioxide (CO2).

These phenomena could be the canaries in the coal mine: the forerunners of damaging, some say even potentially catastrophic, changes to the world's climate system.

Such is the backdrop to the November 6-17 meeting of the UN Framework Convention on Climate Change (UNFCCC), the parent of the Kyoto Protocol on curbing dangerous greenhouse gases.

"What was forecast back in 1990 is being confirmed today," said Jean Jouzel, a French expert who is a member of the Intergovernmental Panel on Climate Change (IPCC), the world's foremost scientific authority on global warming.

"Surface temperatures are rising by around 0.2 C (0.35 F) a decade. On top of that the effects of climate change are now visible. The skeptics are seeing their arguments melt like ice in the sun."

The IPCC was set up in 1988 by the World Meteorological Organisation (WMO) and the UN Environment Programme (UNEP) to provide neutral, science-based assessments on climate change.

Its last assessment was published in early 2001 and confirmed that global warming was underway. The next report is due in early 2007.

"We get together to update our knowledge every six years, assessing certainties and uncertainties. I don't know of any other issue where an effort of this magnitude is made," says French researcher Valerie Masson-Delmotte, who is contributing to a chapter on the climate in the past.

The 2001 IPCC report suggested that by 2100, the mean global temperature will have risen by between 1.4 and 5.8 C (2.5 and 10.4 F).

Since then, climate science has leapt ahead, both in terms of the depth and range of research and the tools, especially computer power, available to do it.

The latest lab simulations do not point to any significant shift in temperature rise from the 2001 forecast, said Jouzel.

But temperature is only one factor in an equation whose complexity, it is now emerging, is far greater than was previously thought.

The newest research says that a bland global figure of temperature rise will mask wide regional variations -- which in turn will affect winds and rainfall patterns and thus fuel the risk of regional droughts and floods.

Just as worrying is evidence that triggers have been unleashed which could amplify global warming: in effect, creating a vicious circle.

These so-called positive feedbacks include the release of methane that had been locked for millennia in the frozen soil of northern Siberia, and the loss of glaciers and snow cover. Ice and snow are white and thus reflect the Sun -- strip away that cover and the exposed soil, because it is dark, traps the heat.

Just as depressing is the realisation that the global warming machine will work for years and years to come.

If levels of greenhouse gases miraculously stabilised tomorrow, there is already so much carbon in the atmosphere that the temperature will continue to rise until 2300, said Serge Planton, an IPCC member who also heads climate research at the French weather agency Meteo-France.

Even though knowledge about global warming has advanced enormously, there remain significant areas of doubt, debate or ignorance.

These areas include the health of Antarctica; whether global warming will make hurricanes and other storms more vicious or frequent; and the role of the deep oceans in the highly complex interchange of heat.

The UNFCCC meeting in Nairobi will gather politicians for talks to gear up the Kyoto Protocol, a treaty with a flawed and troubled history, to meet the challenge.

Thousands of grassroots campaigners will take part, as will representatives from businesses in the fast-growing sectors of renewable energy, carbon trading and adaptation to climate change.

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